At this stage of increasing attention to new regeneration energy around the world, an organic photovoltaic cells (OPVs) having potential as future energy and various advantages are receiving attention. The OPVs can be manufactured in a thin film and at a low price, compared to inorganic photovoltaic cells using silicon, and may be applied to future various flexible devices in various ways.
A conventional OPV may include an anode, a hole extraction layer, a light active layer, and a cathode. The light irradiated to the OPVs may be separated into electrons and holes in the light active layer. The holes may be extracted through the anode via the hole extraction layer, and the electrons may be extracted through the cathode.
To solve issues of high efficiency, a long life span, and a simple device structure, researches on inverted OPVs using metal oxides such as TiO2, ZrO2, and ZnO are on the rise as the most representative solutions which are stable in the air and can be applied to an R2R process.
In the inverted device, in contrast with a general OPV device structure in which holes are extracted through a transparent electrode such as an indium tin oxide (ITO), electrons are extracted through the transparent electrode (e.g., ITO or FTO) to serve as a cathode, and anodes generally use a metal such as Au or Ag.
Due to such a structure, the inverted device may not use a highly-reactive electron extraction electrode (that is, a cathode) used in the general OPV device, a metal such as Ca, Ba, or Li, but may use materials having no reactivity to air or moisture because both of the anode and cathode have high work functions. Although organic materials may be used as an electron extraction layer of an inverted OPV device, particularly, since a metal oxide has high transparency in a visible region and high charge transport capability, and is stable in the air, there are various researches for applying such a metal oxide formed in a solution process to the inverted device.
However, when a conventional oxide electrode such as ITO or FTO, which is disposed on a glass substrate, is bent so as to have a crack in a thin film, it cannot serve as an electrode any more. In addition, although the conventional glass substrate is used since a substrate should also stand a process of depositing a metal oxide performed in a high temperature process at 200° C. or more, the glass substrate is not flexible. Accordingly, it is necessary to use a substrate and an electrode, which has excellent mechanical strength to be bendable and can endure in a high temperature process of 200° C. or more. As such a substrate, a metal foil may be used, but the prior art disclosed that when the metal foil is used, a device is realized by further depositing an electrode after forming an insulating planarization layer, or a device having a complicated structure is realized by further depositing a metal serving as a planarization layer and a reflective conductive layer on the metal foil.